--- Daniele Gratteri <firstname.lastname@example.org> wrote: > Maybe it is a stupid question: a 'pull up' resistor is a normal resistor > simply connected between Vcc and the signal line or I have to ask for a > specific type of resistor? It's not a stupid question so much as an english-language question. In this case "pull-up" refers to the job that it is doing, not what physical kind of component it is. A "normally open" or "normally closed" switch refers to what kind of switch it is. You do, I think, understand what a pull-up resistor is: a resistor (typically in the range of a few K ohms) connected between a signal and Vcc. It holds the signal clearly at a logical "high" signal, which, for TTL is, ISTR between 2.8 and 5.0VDC. Common values include 2.2K Ohms and 4.7K Ohms. I have also seen 1.2K Ohms. Among other things, the resistor prevents a direct path between Vcc and Ground (Earth) preventing circuit damage in typical cases. You normally want them because some chips do not like to have their inputs floating. They want to be high or low, but not hanging in mid-air. -ethan ===== Visit "The Seventh Continent" http://penguincentral.com/penguincentral.html __________________________________________________ Do You Yahoo!? Yahoo! Sports - Coverage of the 2002 Olympic Games http://sports.yahoo.com Message was sent through the cbm-hackers mailing list
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